Is this truly a word, or is it more accurately described as a phrase? I’m imagining that potentially the に is a particle instead of being okurigana.

On that note, I’m a little confused about what constitutes valid use of okurigana. My initial understanding is that Japanese words are A: A single Kanji. B: Compound words (jukugo) composed of multiple kanji. C: Words with kanji stems, and okurigana dangling off the end.

Something that doesn’t fit my mapping though, is words composed of multiple kanji, with hiragana between the kanji instead of at the end. Are these words still classified as jukugo, or are they a different class of word? Also, in WaniKani some of these words are really phrases where the hiragana are just particles. Is this sometimes the case and sometimes not the case?

間に合う is definitely more like a word than a phrase, in this case, at least in my opinion. But that doesn’t necessarily make に okurigana, I’m not sure. I get your confusion about the vagueness of the distinctions, but that’s just something that comes with translation in any language pair.

Edit: I think 間に合う is definitely more like a phrase…に+verb is a construct that can be a phrasing / idiom. Other examples are 頭にくる or a whole bunch of 気 idioms like 気にする、気になる…アルク is good for looking up things that may seem like a phrase.

Someone actually just posed this question in another thread with the example 入り口（いりぐち). Wanikani teaches the reading for this with the り in between the two kanji characters but it can also be seen as 入口 without any hiragana. いり and ぐち are both kunyomi readings so this is techinically non jukugo.

Another example is 「締切」 and this is how wanikani teaches it. This also uses the kunyomi readings and you can see in jisho that alternate readings are 締め切り・締切り which would be non-jukugo.

Edit: I think 間に合う is definitely more like a phrase…に+verb is a construct that can be a phrasing / idiom.

In my mind, the “word versus phrase” distinction is along the lines of “does it get used as its own unit of language or are people constructing it on the fly.” Like, 見に行く is something that get uttered countless times per day in Japan, but it strikes me as people constructing it, where as 間に合う feels like one unit.

The 気 idioms are were I first started thinking about this issue. For example: 気を付けて means to take care, but I think a more literal translation would be “to attach to the energy”, where energy can of be thought of as “good and proper”. It follows from there that you are attaching yourself to the good and proper way of doing something i.e. doing something carefully. For this particular case I assumed it had to be an idiom, because of the direct object marker. With に however, I can’t so safely assume either way.

The reason I care about the distinction, is knowing these rules helps me properly parse Japanese. Back when I only knew hiragana, I was really frustrated because I couldn’t 100% tell where one word ended and another begins. If all words take the form [Kanji], [kanji][kanji][kanji…], [kanji][hiragana], then parsing out the individual words becomes much more consistent: whenever you see a kanji that isn’t directly preceded by another kanji, you know a new word is starting. If hiragana can appear any/everywhere in a word, that makes things much more ambiguous >_>.